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1.
The Qinling‐Tongbai‐Dabie‐Sulu orogenic belt comprises a Palaeozoic accretion‐dominated system in the north and a Mesozoic collision‐dominated system in the south. A combined petrological and geochronological study of the medium‐to‐high grade metamorphic rocks from the diverse Palaeozoic tectonic units in the Tongbai orogen was undertaken to help elucidate the origins of Triassic ultrahigh‐pressure metamorphism and collision dynamics between the Sino‐Korean and Yangtze cratons. Peak metamorphic conditions are 570–610 °C and 9.3–11.2 kbar for the lower unit of the Kuanping Group, 630–650 °C and 6.6–8.9 kbar for the upper unit of the Kuanping Group, 550–600 °C and 6.3–7.7 kbar for the Erlangping Group, 770–830 °C and 6.9–8.5 kbar for the Qinling Group and 660–720 °C and 9.1–11.5 kbar for the Guishan complex. Reaction textures and garnet compositions indicate clockwise P–T paths for the amphibolite facies rocks of the Kuanping Group and Guishan complex, and an anticlockwise P–T path for the granulite facies rocks of the Qinling Group. Sensitive high‐resolution ion microprobe U–Pb zircon dating on metamorphic rocks and deformed granite/pegmatites revealed two major Palaeozoic tectonometamorphic events. (i) During the Silurian‐Devonian (c. 440–400 Ma), the Qinling continental arc and Erlangping intra‐oceanic arc collided with the Sino‐Korean craton. The emplacement of the Huanggang diorite complex resulted in an inverted thermal gradient in the underlying Kuanping Group and subsequent thermal relaxation during the exhumation. Meanwhile, the oceanic subduction beneath the Qinling continental arc produced magmatic underplating and intrusion, leading to granulite facies metamorphism followed by a near‐isobaric cooling path. (ii) During the Carboniferous (c. 340–310 Ma), the northward subduction of the Palaeo‐Tethyan ocean generated a medium P/T Guishan complex in the hangingwall and a high P/T Xiongdian eclogite belt in the footwall. The Guishan complex and Xiongdian eclogite belt are therefore considered to be paired metamorphic belts. Subsequent separation of the paired belts is inferred to be related to the juxtaposition of the Carboniferous eclogites with the Triassic HP metamorphic complex during continental subduction and exhumation.  相似文献   

2.
东秦岭二郎坪弧后盆地双向式俯冲特征   总被引：10，自引：0，他引：10  
二郎坪弧后盆地是北秦岭早生古代活动大陆边缘沟－弧－盆系统的重要组成部分,现今二郎坪岩群是古弧后盆地的物质残存,记录了盆地演化方式和过程,沉积建造和岩浆作用研究发同,在二郎坪弧后盆地南北两侧各发育一套活动型陆缘沉积体系和一系列府冲型花岗岩,变形构造解析反映出主造山期早期沿弧后盆地两侧各形成一套韧性推覆构造系,并具对冲型几何学样式,为俯冲带典型构造,综合分析表明,弧后盆地在造山早期分别俯冲于南部秦岭古岛弧和北部宽坪古陆之下,具双向式俯冲特征。  相似文献   

3.
《Gondwana Research》2013,24(4):1402-1428
The formation of collisional orogens is a prominent feature in convergent plate margins. It is generally a complex process involving multistage tectonism of compression and extension due to continental subduction and collision. The Paleozoic convergence between the South China Block (SCB) and the North China Block (NCB) is associated with a series of tectonic processes such as oceanic subduction, terrane accretion and continental collision, resulting in the Qinling–Tongbai–Hong'an–Dabie–Sulu orogenic belt. While the arc–continent collision orogeny is significant during the Paleozoic in the Qinling–Tongbai–Hong'an orogens of central China, the continent–continent collision orogeny is prominent during the early Mesozoic in the Dabie–Sulu orogens of east-central China. This article presents an overview of regional geology, geochronology and geochemistry for the composite orogenic belt. The Qinling–Tongbai–Hong'an orogens exhibit the early Paleozoic HP–UHP metamorphism, the Carboniferous HP metamorphism and the Paleozoic arc-type magmatism, but the three tectonothermal events are absent in the Dabie–Sulu orogens. The Triassic UHP metamorphism is prominent in the Dabie–Sulu orogens, but it is absent in the Qinling–Tongbai orogens. The Hong'an orogen records both the HP and UHP metamorphism of Triassic age, and collided continental margins contain both the juvenile and ancient crustal rocks. So do in the Qinling and Tongbai orogens. In contrast, only ancient crustal rocks were involved in the UHP metamorphism in the Dabie–Sulu orogenic belt, without involvement of the juvenile arc crust. On the other hand, the deformed and low-grade metamorphosed accretionary wedge was developed on the passive continental margin during subduction in the late Permian to early Triassic along the northern margin of the Dabie–Sulu orogenic belt, and it was developed on the passive oceanic margin during subduction in the early Paleozoic along the northern margin of the Qinling orogen.Three episodes of arc–continent collision are suggested to occur during the Paleozoic continental convergence between the SCB and NCB. The first episode of arc–continent collision is caused by northward subduction of the North Qinling unit beneath the Erlangping unit, resulting in UHP metamorphism at ca. 480–490 Ma and the accretion of the North Qinling unit to the NCB. The second episode of arc–continent collision is caused by northward subduction of the Prototethyan oceanic crust beneath an Andes-type continental arc, leading to granulite-facies metamorphism at ca. 420–430 Ma and the accretion of the Shangdan arc terrane to the NCB and reworking of the North Qinling, Erlangping and Kuanping units. The third episode of arc–continent collision is caused by northward subduction of the Paleotethyan oceanic crust, resulting in the HP eclogite-facies metamorphism at ca. 310 Ma in the Hong'an orogen and low-P metamorphism in the Qinling–Tongbai orogens as well as crustal accretion to the NCB. The closure of backarc basins is also associated with the arc–continent collision processes, with the possible cause for granulite-facies metamorphism. The massive continental subduction of the SCB beneath the NCB took place in the Triassic with the final continent–continent collision and UHP metamorphism at ca. 225–240 Ma. Therefore, the Qinling–Tongbai–Hong'an–Dabie–Sulu orogenic belt records the development of plate tectonics from oceanic subduction and arc-type magmatism to arc–continent and continent–continent collision.  相似文献   

4.
Qinling ore belt is the largest known molybdenum belt in the world with a total reserve of >5 Mt of Mo metal. Based on the geochemical behaviour of Mo, the structural settings of the Qinling orogenic belt, and geological events in eastern China, we propose that tectonic settings are of critical importance to the formation of these ore deposits. Molybdenum is very rare in the earth with an abundance of ～0.8 ppm in the continental crust. Both surface- and magmatic-hydrothermal enrichment processes are required for Mo mineralization. It can be easily oxidized to form water-soluble MoO4 – in the surface environment, especially in the Phanaerozoic, and then precipitated under anoxic conditions. Therefore, closed or semi-closed water bodies with large catchment areas and high chemical erosion rates are the most favourable locations for Mo-enriched sediments. The Qinling orogenic belt was located in the tropics during crustal collisions, such that the chemical erosion was presumably intense, whereas the Erlangping back-arc basin was probably a closed or semi-closed water body as a result of plate convergence. More than 90% of the Mo reserves so far discovered in the Qinling molybdenum belt are associated with the Palaeozoic Erlangping back-arc basin. Compiled Re–Os isotopic ages for porphyry deposits (including several carbonate vein deposits) that have been dated show peaks during 220 million years (>0.32 Mt), 145 million years (>?3.5 Mt), and 115 million years (>?0.84 Mt), which correlate well with the three major episodes of granitoid magmatism since the Triassic. The ～220 million year episode of mineralization, represented by the Huanglongpu carbonate vein-type deposit and the Wenquan porphyry deposit, coincided with the formation of the South Qinling syn-orogenic granites as well as the Dabie ultrahigh-pressure metamorphic rocks, suggests a genetic relationship with the collision between South and North China Blocks. The ～145 Ma porphyry Mo deposits, representing the main mineralization, are attributed to reactivation by ridge subduction along the lower Yangtze River belt to the east of the Qinling orogen ～150–140 Ma. The ～115 Ma Mo deposits likely reflect slab rollback of the northwestwards subducting Pacific plate ～125–110 Ma.  相似文献   

5.
In this study, we challenge the multiple collision model for the tectonic evolution of the Neoproterozoic Ribeira Belt in Southeastern Brazil. New U–Pb SHRIMP data reveal Palaeoproterozoic (2153 ± 15 Ma) and Cryogenian (783 ± 6 and 768 ± 8 Ma) granitic rocks in the Embu Domain, and detrital zircon data of metasedimentary units from the Embu and Costeiro domains suggest a coherent tectonic evolution for the whole Ribeira Belt. Rather than by multiple collisions, these data are best explained by a simpler tectonic model involving continent (craton)‐volcanic arc collisions in the Dom Feliciano and Brasilia belts that led to intracontinental crustal thickening of the adjacent thinned hinterland (Ribeira Belt) at ~640–610 Ma, followed by widespread post‐collisional magmatism and rift‐related sedimentation at ~600–540 Ma. We suggest that intracontinental orogeny is a relevant process during supercontinent assembly, as illustrated here by the evolution of significant parts of the Brasiliano orogen.  相似文献   

6.
华北地块南部晚古生代—三叠纪盆山耦合关系   总被引：9，自引：0，他引：9       下载免费PDF全文
华北地块南部的晚古生代至中生代初期发育有多种类型的沉积盆地,其形成演化直接受控于秦岭造山带的主造山作用过程,泥盆纪－石炭纪是岭与华北地块的点接触碰撞时期,古秦岭洋和二郎坪弧后盆地同期逐步消亡,深化为陆壳基础上的残余海盆地及残余弧后盆地,二叠为面接触碰撞阶段,豫西小秦岭岭段首先隆升,成为向北的物源区,在商丹－北淮阳主缝合带及其弧后残余盆地消亡的同时,华北地块南部形成盆地,并成为旱二叠世华北陆表海的沉积中心,秦岭与华北地块全面碰撞发生于三叠纪,在造山变质变形广泛活动的背景下,华北地块则形成了统一的大型坳陷型盆地。  相似文献   

7.
The Qinling orogenic belt experienced multiple phases of orogenesis during the Palaeozoic. Unraveling the timing and P–T conditions of these events is the key to understanding the convergence processes between the South China and the North China Blocks. The Songshugou Complex, located in the southern part of the North Qinling orogenic belt, has registered multistage metamorphism in Palaeozoic, and thus potentially provides insights into the tectonic evolution of the Qinling orogenic belt. In this study, three metabasic rocks (a garnet pyroxenite, a garnet amphibolite and a gneissic amphibolite) from the Songshugou Complex were selected for petrological study and zircon and titanite U–Pb dating. Our results show that the metabasic rocks experienced three metamorphic events during the Palaeozoic. The first metamorphic event (M1) is characterized by high pressure conditions. Two zircon grains in equilibrium with garnet and in absence of plagioclase were recognized from the garnet pyroxenite sample. They yielded Ti-in-zircon temperatures of 660–851 °C at ∼12.0 kbar and a weighted mean age of 498 ± 15 Ma, providing the constraints on the temperature and timing of prograde or peak metamorphism (M1-1). Zircons that are inequilibrium with garnet from the garnet pyroxenite and the garnet amphibolite gave U–Pb ages of 494 ± 9 Ma and 484 ± 4 Ma, and Ti-in-zircon temperatures of 793 ± 33 °C and 738 ± 18 °C, respectively. Thus, these zircons were formed on the retrograde amphibolite-facies conditions at ∼8.0 kbar (M1-2). Titanite inclusions were found in actinolite cores of zoned amphibole from the garnet amphibolite. They yielded a U–Pb age of ∼470 Ma and Zr-in-titanite temperature of 676 ± 23 °C at pressure of ∼7.0 kbar, suggesting that the amphibolite-facies retrogression perhaps persisted to ∼470 Ma.Weakly zoned zircons from the garnet amphibolite and inclusion-free titanites from the garnet pyroxenite gave consistent U–Pb ages of 418 ± 5 Ma and 423 ± 10 Ma, and Ti-in-zircon temperature of 742 ± 26 °C and Zr-in-titanite temperature of 764 ± 18 °C at ∼7.0 kbar, respectively. It is suggested that a heating event (M2) is registered by a subsequent phase of amphibolite-facies metamorphism. The ilmenite-bearing titanite crystals from the garnet pyroxenite yielded a U–Pb age of 352 ± 4 Ma, recording a late thermal event (M3).On the basis of combined petrological and geochronological results, we propose a revised tectonic model for the North Qinling orogeny in Palaeozoic. The high pressure granulites were formed by the northward subduction of the Shangdan oceanic slab and the arc-continent collision at ca. 500 Ma. Their exhumation happened at ca. 494–484 Ma as a result of slab breakoff. Subsequent amphibolite-facies metamorphism dated at ca. 440–420 Ma are coeval with the widespread magmatism in the North Qinling Terrane, which are likely caused by the reinitiation northward-subducted of Shangdan oceanic slab. At ca. 350 Ma, the North Qinling Terrane was likely affected by another thermal overprinting event.  相似文献   

8.
By comparing detrital zircon U–Pb age spectra of coeval fore‐arc and back‐/intra‐arc basin sandstones, we identified the overall distributary pattern of terrigenous clastic material within the Cretaceous arc system of SW Japan. Abundant Proterozoic (c. 1500–2500 Ma) detrital grains from the interior of East Asia are present in the Cretaceous intra‐arc basin. However, after a barrier mountain range formed during batholith emplacement, Proterozoic clastics were rarely transported into the fore‐arc domain. Episodic batholith formation in Pacific‐type orogens likely played a major role in controlling terrigenous supply routes between coeval back‐arc and fore‐arc domains. The Cretaceous orogen in Japan thus provides a good template for analysing the tectono‐sedimentary development of other arc‐related basins.  相似文献   

9.
The amalgamation of South (SCB) and North China Blocks (NCB) along the Qinling‐Dabie orogenic belt involved several stages of high pressure (HP)‐ultra high pressure (UHP) metamorphism. The new discovery of UHP metamorphic rocks in the North Qinling (NQ) terrane can provide valuable information on this process. However, no precise age for the UHP metamorphism in the NQ terrane has been documented yet, and thus hinders deciphering of the evolution of the whole Qinling‐Dabie‐Sulu orogenic belt. This article reports an integrated study of U–Pb age, trace element, mineral inclusion and Hf isotope composition of zircon from an eclogite, a quartz vein and a schist in the NQ terrane. The zircon cores in the eclogite are characterized by oscillatory zoning or weak zoning, high Th/U and 176Lu/177Hf ratios, pronounced Eu anomalies and steep heavy rare earth element (HREE) patterns. The zircon cores yield an age of 796 ± 13 Ma, which is taken as the protolith formation age of the eclogite, and implies that the NQ terrane may belong to the SCB before it collided with the NCB. The ?Hf(t) values vary from ?11.3 to 3.2 and corresponding two‐stage Hf model ages are 2402 to 1495 Ma, suggesting the protolith was derived from an enriched mantle. In contrast, the metamorphic zircon rims show no zoning or weak zoning, very low Th/U and 176Lu/177Hf ratios, insignificant Eu anomalies and flat HREE patterns. They contain inclusions of garnet, omphacite and phengite, suggesting that the metamorphic zircon formed under eclogite facies metamorphic conditions, and their weighted mean 206Pb/238U age of 485.9 ± 3.8 Ma was interpreted to date the timing of the eclogite facies metamorphism. Zircon in the quartz vein is characterized by perfect euhedral habit, some oscillatory zoning, low Th/U ratios and variable HREE contents. It yields a weighted mean U–Pb age of 480.5 ± 2.5 Ma, which registers the age of fluid activity during exhumation. Zircon in the schist is mostly detrital and U–Pb age peaks at c. 1950 to 1850, 1800 to 1600, 1560 to 1460 and 1400 to 1260 Ma with an oldest grain of 2517 Ma, also suggesting that the NQ terrane may have an affinity to the SCB. Accordingly, the amalgamation between the SCB and the NCB is a multistage process that spans c. 300 Myr, which includes: the formation of the Erlangping intra‐oceanic arc zone onto the NCB before c. 490 Ma, the c. 485 Ma crustal subduction and UHP metamorphism of the NQ terrane, the c. 430 Ma arc‐continent collision and granulite facies metamorphism, the 420 to 400 Ma extension and rifting in relation to the opening of the Palaeo‐Tethyan ocean, the c. 310 Ma HP eclogite facies metamorphism of oceanic crust and associated continental basement, and the final 250 to 220 Ma continental subduction and HP–UHP metamorphism.  相似文献   

10.
秦岭商-丹缝合带是分隔北秦岭早古生代造山带和南秦岭晚古生代造山带的地质界线,其中的丹凤蛇绿岩被认为代表了秦岭地区早古生代的洋壳残片。迄今,前人已经提出多种模式来解释丹凤蛇绿岩成因和构造背景(如:岛弧、洋岛和成熟的大洋等)。然而,这些单一的构造演化模式却很难解释两个基本事实:(1)不同类型镁铁质岩(如N-MORB、E-MORB和IAT等)的穿时性分布;(2)几乎所有的早古生代镁铁质岩都显示出多种构造环境的叠加。对陕西太白鹦鸽嘴地区一条具有较完整层序的蛇绿岩剖面研究发现,剖面中存在HTI型(TiO2:1.21%～1.56%)和LTI(TiO2:0.09%～0.35%)两种类型的镁铁质岩(包括玄武岩和辉长岩),HTI型镁铁质岩具有LREE亏损,没有Nb、Ta负异常等的E-MORB特征;LTI具有LREE富集,Nb、Ta负异常的IAT特征。地球化学显示二者的源区均为北秦岭岩石圈地幔楔。本文获得鹦哥嘴蛇绿岩两个LTI型辉长岩锆石U-Pb年龄分别为523.8±1.3Ma和474.3±1.4Ma。认为秦岭早古生代蛇绿岩应是SSZ环境下多阶段演化的结果:第一阶段:约524Ma,秦岭洋盆向北俯冲开始。俯冲板片的脱水作用使熔融温度降低,形成的流体交代地幔楔,在北秦岭南缘产生了一个不成熟的岛弧;第二阶段:先存岛弧裂开阶段,约524～474Ma。秦岭洋壳的持续俯冲,在先形成的岛弧上拉张出了弧间盆地,形成了主要由轻稀土亏损、高Ti拉斑玄武岩和辉长岩组成的E-MORB型岩石组合;第三阶段:弧前盆地闭合阶段,474Ma之后。在这个阶段新生的弧间盆地闭合,俯冲洋壳携带的深海沉积物与北秦岭岩石圈地幔楔相互作用形成了北秦岭李子园的玻安岩。秦岭早古生代蛇绿岩的多阶段成因是典型特提斯构造域演化特征在秦岭地区的重现。  相似文献   

11.
A combined study of petrology and geochemistry was carried out for granulites from the Tongbai orogen in central China. The results reveal the tectonic evolution from collisional thickening to extensional thinning of the lithosphere at the convergent plate boundary. Petrographic observations, zircon U–Pb dating, and pseudosection calculations indicate that the granulites underwent four metamorphic stages, which are categorized into two cycles. The first cycle occurred at 490–450 Ma and involves high-P (HP) metamorphism (M1) at 785–815°C and 10–14 kbar followed by decompressional heating to 840–880°C and 8–9 kbar for medium-pressure granulite facies metamorphism (M2), defining a clockwise P–T path. The high pressure is indicated by the occurrence of inclusions of rutile+kyanite+K-feldspar in the garnet mantle. The second cycle occurred at c. 440 Ma and shows an anticlockwise P–T path with continuous heating to ultrahigh-temperature (UHT) metamorphism (M3) at 890–980°C and 9–11 kbar, followed by decompressional cooling to 740–880°C and 7–9 kbar (M4) till 405 Ma. The HP metamorphism is synchronous with the ultrahigh-pressure eclogite facies metamorphism in the Qinling orogen, indicating its relevance to the continental collision in the Cambrian. The UHT metamorphism took place at reduced pressures, indicating thinning of the collision-thickened orogenic lithosphere. Therefore, the Tongbai orogen was initially thickened by the collisional orogeny and then thinned, possibly as a result of foundering of the orogenic root. Such tectonic evolution may be common in collisional orogens where compression during continental collision switched to extension during continental rifting.  相似文献   

12.
The Ross orogen of Antarctica is an extensive (>3000 km‐long) belt of deformed and metamorphosed sedimentary rocks and granitoid batholiths, which formed during convergence and subduction of palaeo‐Pacific lithosphere beneath East Gondwana in the Neoproterozoic–early Palaeozoic. Despite its prominent role in Gondwanan convergent tectonics, and a well‐established magmatic record, relatively little is known about the metamorphic rocks in the Ross orogen. A combination of garnet Lu–Hf and monazite U–Pb (measured by laser‐ablation split‐stream ICP‐MS) geochronology reveals a protracted metamorphic history of metapelites and garnet amphibolites from a major segment of the orogen. Additionally, direct dating of a common rock‐forming mineral (garnet) and accessory mineral (monazite) allows us to test assumptions that are commonly used when linking accessory mineral geochronology to rock‐forming mineral reactions. Petrography, mineral zoning, thermobarometry and pseudosection modelling reveal a Barrovian‐style prograde path, reaching temperatures of ~610–680 °C. Despite near‐complete diffusional resetting of garnet major element zoning, the garnet retains strong rare earth element zoning and preserves Lu–Hf dates that range from c. 616–572 Ma. Conversely, monazite in the rocks was extensively recrystallized, with concordant dates that span from c. 610–500 Ma, and retain only vestigial cores. Monazite cores yield dates that overlap with the garnet Lu–Hf dates and typically have low‐Y and heavy rare earth element (HREE) concentrations, corroborating interpretations of low‐Y and low‐HREE monazite domains as records of synchronous garnet growth. However, ratios of REE concentrations in garnet and monazite do not consistently match previously reported partition coefficients for the REE between these two minerals. High‐Y monazite inclusions within pristine, crack‐free garnet yield U–Pb dates significantly younger than the Lu–Hf dates for the same samples, indicating recrystallization of monazite within garnet. The recrystallization of high‐Y and high‐HREE monazite domains over >50 Ma likely records either punctuated thermal pulses or prolonged residence at relatively high temperatures (up to ~610–680 °C) driving monazite recrystallization. One c. 616 Ma garnet Lu–Hf date and several c. 610–600 Ma monazite U–Pb dates are tentatively interpreted as records of the onset of tectonism metamorphism in the Ross orogeny, with a more robust constraint from the other Lu–Hf dates (c. 588–572 Ma) and numerous c. 590–570 Ma monazite U–Pb dates. The data are consistent with a tectonic model that involves shortening and thickening prior to widespread magmatism in the vicinity of the study area. The early tectonic history of the Ross orogen, recorded in metamorphic rocks, was broadly synchronous with Gondwana‐wide collisional Pan‐African orogenies.  相似文献   

13.
The Vohibory Block of south‐western Madagascar is part of the East African Orogen, the formation of which is related to the assembly of the Gondwana supercontinent. It is dominated by metabasic rocks, which have chemical compositions similar to those of recent basalts from a mid‐ocean ridge, back‐arc setting and island‐arc setting. The age of formation of protolith basalts has been dated at 850–700 Ma by U–Pb SHRIMP analysis of magmatic cores in zircon, pointing to an origin related to the Neoproterozoic Mozambique Ocean. The metabasic rocks are interpreted as representing components of an island arc with an associated back‐arc basin. In the early stage of the Pan‐African orogeny, these rocks experienced high‐pressure amphibolite to granulite facies metamorphism (9–12 kbar, 750–880 °C), dated at 612 ± 5 Ma from metamorphic rims in zircon. The metamorphism was most likely related to accretion of the arc terrane to the margin of the Azania microcontinent (Proto‐Madagascar) and closure of the back‐arc basin. The main metamorphism is significantly older than high‐temperature metamorphism in other tectonic units of southern Madagascar, indicating a distinct tectono‐metamorphic history.  相似文献   

14.
The Arthur River Complex is a suite of gabbroic to dioritic orthogneisses in northern Fiordland, New Zealand. The Arthur River Complex separates rocks of the Median Tectonic Zone, a Mesozoic island arc complex, from Palaeozoic rocks of the palaeo‐Pacific Gondwana margin, and is itself intruded by the Western Fiordland Orthogneiss. New SHRIMP U/Pb single zircon data are presented for magmatic, metamorphic and deformation events in the Arthur River Complex and adjacent rocks from northern Fiordland. The Arthur River Complex orthogneisses and dykes are dominated by magmatic zircon dated at 136–129 Ma. A dioritic orthogneiss that occurs along the eastern margin of the Complex is dated at 154.4 ± 3.6 Ma and predates adjacent plutons of the Median Tectonic Zone. Rims on zircon cores from this sample record a thermal event at c. 120 Ma, attributed to the emplacement of the Western Fiordland Orthogneiss. Migmatitic Palaeozoic orthogneiss from the Arthur River Complex (346 ± 6 Ma) is interpreted as deformed wall rock. Very fine rims (5–20 µm) also indicate a metamorphic age of c. 120–110 Ma. A post‐tectonic pegmatite (81.8 ± 1.8 Ma) may be related to phases of crustal extension associated with the opening of the Tasman Sea. The Arthur River Complex is interpreted as a batholith, emplaced at mid‐crustal levels and then buried to deep crustal levels due to convergence of the Median Tectonic Zone arc and the continental margin.  相似文献   

15.
The Jiajiwaxi pluton in the southern portion of the West Kunlun Range can be divided into two collision–related intrusive rock series, i.e., a gabbro–quartz diorite–granodiorite series that formed at 224±2.0 Ma and a monzonitic granite–syenogranite series that formed at 222±2.0 Ma. The systematic analysis of zircon U-Pb geochronology and bulk geochemistry is used to discuss the magmatic origin(material source and thermal source), tectonic setting, genesis and geotectonic implications of these rocks. The results of this analysis indicate that the parent magma of the first series, representing a transition from I-type to S-type granites, formed from thermally triggered partial melting of deep crustal components in an early island–arc–type igneous complex, similar to an I-type granite, during the continental collision orogenic stage. The parent magma of the second series, corresponding to an S-type granite, formed from the partial melting of forearc accretionary wedge sediments in a subduction zone in the late Palaeozoic–Triassic. During continued collision, the second series magma was emplaced into the first series pluton along a central fault zone in the original island arc region, forming an immiscible puncture-type complex. The deep tectonothermal events associated with the continent–continent collision during the orogenic cycle are constrained by the compositions and origins of the two series. The new information provided by this paper will aid in future research into the dynamic mechanisms affecting magmatic evolution in the West Kunlun orogenic belt.  相似文献   

16.
北秦岭小寨变质沉积岩系的地质特征及其构造意义   总被引：1，自引：0，他引：1  
李亚林  王根宝 《沉积学报》1999,17(4):596-600
原岩恢复、沉积建造及变形变质综合研究表明,北秦岭小寨变质沉积岩系属活动陆缘性质沉积建造,形成于二郎坪弧后盆地消减俯冲带的海沟盆地-海沟斜坡环境,是古俯冲带的重要证据之一,其变形序列反映了弧后盆地构造演化过程,并与构造混杂岩、俯冲型花岗岩及高压变质带一起构成相对完整的古俯冲带标志,为探讨秦岭古生代板块构造演化提供了重要信息。  相似文献   

17.
李兴辉  郭安林  李侃  高春云 《地质通报》2014,33(9):1353-1362
秦岭造山带在印支造山作用主造山期之后,发育一系列晚三叠世—早侏罗世伸展断陷盆地。选择陕西丹凤北秦岭灵官庙盆地中低绿片岩相的灰绿色中细粒砂岩,进行碎屑锆石LA-ICP-MS U-Pb同位素分析。结果表明,85个以岩浆成因为主的碎屑锆石给出5个年龄组:426~605Ma、661~1174Ma、1494~1789Ma、2113~2261Ma和2826~3298Ma。其中,最年轻的锆石年龄为426Ma±5Ma,最老的锆石年龄为3298Ma±70Ma。主要的年龄峰期为426~605Ma年龄组,其次为661~1174Ma年龄组。这一年龄结构反映出物源区加里东造山期和Grenvillian期岩浆活动的重要影响。年龄谱中缺少中志留世—晚三叠世的锆石,说明普遍发育的印支期岩浆岩体并不构成物源区。通过与现今周缘地体年龄结构对比并结合其他地质证据认为,灵官庙盆地的物源可能主要来自加里东期侵位于二郎坪群、秦岭群中的花岗岩和新元古代宽坪群,少量来自二郎坪群和秦岭群。灵官庙盆地形成之后,盆地内沉积岩遭受了变质变形作用,记录了秦岭造山带在板块构造驱动的造山作用结束后进入了新的陆内造山作用阶段。  相似文献   

18.
The Serbo-Macedonian Massif (SMM) represents a composite crystalline belt within the Eastern European Alpine orogen, outcropping from the Pannonian basin in the north, to the Aegean Sea in the south. The central parts of the massif (i.e. southeastern Serbia, southwestern Bulgaria, eastern Macedonia) consist of the medium- to high-grade Lower Complex, and the low-grade Vlasina Unit. New results of U–Pb LA-ICP-MS analyses, coupled with geochemical analyses of Hf isotopes on magmatic and detrital zircons, and main and trace element concentrations in whole-rock samples suggest that the central SMM and the basement of the adjacent units (i.e. Eastern Veles series and Struma Unit) originated in the central parts of the northern margin of Gondwana. These data provided a basis for a revised tectonic model of the evolution of the SMM from the late Ediacaran to the Early Triassic.The earliest magmatism in the Lower Complex, Vlasina Unit and the basement of Struma Unit is related to the activity along the late Cadomian magmatic arc (562–522 Ma). Subsequent stage of early Palaeozoic igneous activity is associated with the reactivation of subduction below the Lower Complex and the Eastern Veles series during the Early Ordovician (490–478 Ma), emplacement of mafic dykes in the Lower Complex due to aborted rifting in the Middle Ordovician (472–456 Ma), and felsic within-plate magmatism in the early Silurian (439 ± 2 Ma). The third magmatic stage is represented by Carboniferous late to post-collisional granites (328–304 Ma). These granites intrude the gneisses of the Lower Complex, in which the youngest deformed igneous rocks are of early Silurian age, thus constraining the high-strain deformation and peak metamorphism to the Variscan orogeny. The Permian–Triassic (255–253 Ma) stage of late- to post-collisional and within-plate felsic magmatism is related to the opening of the Mesozoic Tethys.  相似文献   

19.
The Qilian–Qaidam orogenic belt at the northern edge of the Tibetan Plateau has received increasing attention as it recorded a complete history from continental breakup to opening and closure of ocean basin, and to the ultimate continental collision in the time period from the Neoproterozoic to the Paleozoic. Determining a geochronological framework of the initiation and termination of the fossil Qilian Ocean subduction in the North Qilian orogenic belt plays an essential role in understanding the whole tectonic process. Dating the high-pressure metamorphic rocks in the North Qilian orogenic belt, such as blueschist and eclogite, is the key in this respect. A blueschist from the southern North Qilian orogenic belt was investigated with a combined metamorphic P–T and U–Pb, Lu–Hf, and Sm–Nd multichronometric approaches. Pseudosection modeling indicates that the blueschist was metamorphosed under peak P–T conditions of 1.4–1.6 GPa and 530–550 °C. Zircon U–Pb ages show no constraints on the metamorphism due to the lack of metamorphic growth of zircon. Lu–Hf and Sm–Nd ages of 466.3 ± 2.0 Ma and 462.2 ± 5.6 Ma were obtained for the blueschist, which is generally consistent with the U–Pb zircon ages of 467–489 Ma for adjacent eclogites. Lutetium and Sm zoning profiles in garnet indicate that the Lu–Hf and Sm–Nd ages are biased toward the formation of the garnet inner rim. The ages are thus interpreted to reflect the time of blueschist-facies metamorphism. Previous 40Ar/39Ar ages of phengitic muscovite from blueschist/eclogite in this area likely represent a cooling age due to the higher peak metamorphic temperature than the argon retention temperature. The differences of peak metamorphic conditions and metamorphic ages between the eclogites and adjacent blueschists indicate that this region likely comprises different tectonic slices, which had distinct P–T histories and underwent high-pressure metamorphism at different times. The initial opening of the Qilian Ocean could trace back to the early Paleozoic, and the ultimate closure of the Qilian Ocean was no earlier than c. 466 Ma.  相似文献   

20.
The Pulan-Xiangquanhe ophiolite in the western Yarlung Tsangpo suture zone of Tibet is investigated for its geochemistry,geochronology,and tectonic implications in detail.Sensitive high resolution ion micro-probe zircon U-Pb dating reveals that diabases in the ophiolite from the three locations of Xugugab,Mapam Yum Co and La'nga Co are dated at 122.3±2.5 Ma,118.8±1.8 Ma and 120.5±1.9 Ma,respectively.These early Cretaceous mafic rocks have Na_2O+K_2O,rare earth element patterns,trace elemental spider diag...  相似文献   

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